Anarchy Online is a massively multiplayer online role-playing game (MMORPG) published and developed by Funcom. Released in the summer of 2001, the game was first in the genre to include a science-fiction setting, dynamic quests, free trials, and in-game advertising. The most ground breaking feature in Anarchy Online, however, was instancing. During its first month of release, many stability, registration, and billing issues hurt public perception of the game. This troubled launch, often echoed by modern reviewers, contrasts with the generally positive critical reception of the game and its expansions; not least was the Shadowlands expansion in 2003 that earned several Editor's Choice awards.

The game's ongoing story revolves around the fictional desert planet Rubi-Ka, the source of a valuable mineral known as "notum". Fighting for military and political power on Rubi-Ka are the Omni-Tek corporation (owners of the planet's thousand-year lease), the separatist Clans, terrorist groups, aliens, and ancient civilizations. The narrative was developed to be played out as a series of virtual role-play events over the course of four years, influenced by the actions of those playing the game. Players assume the roles of new colonists to Rubi-Ka, represented by a persistent 3D virtual world. With no specific objective to win the game, they improve their characters' skill and status over time. This free-form progression leads to social networking, cooperation, and conflict with other players.

After eight years, Anarchy Online has become one of the oldest games in its genre still online. Its "Free Play" program, started in 2004, allows new players indefinite access to the original game in return for viewing in-game advertisements.